This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-212427 filed on Jul. 12, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an automotive air-conditioner that includes a compressor driven by an electric motor powered by an on-board battery and an electric heater powered by the on-board battery.
2. Description of Related Art
In an air-conditioner mounted on an electric vehicle, a compressor of the air-conditioner cannot be driven by an engine. Accordingly, the compressor is driven by an electric motor powered by an on-board battery, and an electric heater is used as a heat source for heating. Examples of the air-conditioner of this kind are disclosed in JP-A-5-229334 and JP-A-10-157445. Usually, a rated voltage of an on-board battery for driving an electric vehicle is high, such as 288 volts, and a terminal voltage of the buttery may abnormally rise to a level much higher than the rated voltage due to various reasons. In case the battery voltage becomes abnormally high, an excessively high current which causes damages in the electric heater is supplied to the electric heater. Further, because the electric heater is overheated in such an occasion, a problem in safety may occur. Though the air-conditioner disclosed in the above publications includes an electric heater, such an overheating problem is not considered, and therefore no solution to that problem is mentioned.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved air-conditioner for use in an electric vehicle, in which adverse effects to an electric heater due to abnormal increase of a battery voltage are eliminated.
The air-conditioner includes a compressor for compressing refrigerant in a refrigeration cycle and an electric heater for heating water circulating through a heater core. The air-conditioner is mounted on a vehicle electrically driven by an on-board battery or a vehicle driven by both of an internal combustion engine and an on-board battery. Both of the electric heater and the compressor are powered by the on-board battery.
The electric heater is switched off when a voltage of the on-board battery reaches a first predetermined level which is considerably higher than a rated voltage of the on-board battery to prevent the electric heater from being overheated. When the voltage of the on-board battery further increases to a second predetermined level, the compressor is also turned off to secure durability of the compressor. Preferably, the first predetermined voltage level is set to a level at which the heater output power becomes about two times of the heater output power obtained at the rated voltage. Preferably, a voltage detector for detecting the on-board battery voltage and a switching circuit for controlling operation of the electric heater are integrally built in an inverter that controls operation of the compressor.
Though a voltage range in which the electric heater is operated is set to a narrower range than that of the compressor, the hot water heated by the electric heater can properly maintain a desired temperature because hot water has a high heat capacity. The electric heater is protected from overheating due to abnormal increase of the voltage of the on-board battery.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.